An Invasion of Monster Girls?
by UberNimrod
Summary: Something strange is going on in Mahora Academy. Intrusions have been detected, but no one can catch the intruders long enough to ask why. The Headmaster has allowed everyone to cosplay before Halloween, but the costumes that people have been using seem a bit too realistic. Crossover between Negima and Monster Girl Encyclopedia.
1. Day Before

Negima is owned by Ken Akamatsu and Kodansha. Whoever created Monster Girl Encyclopedia owns the rest. I am making nothing off this.

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Chapter 0

Day Before

 _._

 _Crap! Mine got away!_

Gandolfini grunted even as he chased the girl dressed as a ninja currently trying to elude him. Seruhiko's telepathic communication meant that this was the only chance he had of identifying whoever it was sneaking around Mahora Academy.

 _Mine is headed south. Towards the bridge._

There had been two of them when they had been discovered, but they had split up when Gandolfini and Seruhiko tried to capture them. Both of them had dodged the Sagitta Magica that he had cast with ease.

 _Anyone nearby to intercept?_

For that matter, they might not be female. But as both had waist-length hair, it was almost certain that both were female. At least in his opinion anyway. He wished he could have gotten a better look at them, but it had been obvious they were well-trained, judging by how quickly they had noticed him and Seruhiko approaching.

 _I am on my way. Keep chasing her south._

'Good. Takamichi is catching up,' he thought. He still believed that he imagined the pointed ears and thin tail he saw when he first discovered them. Although it was becoming increasingly obvious that the tail was indeed real. Especially as it seemed to help whoever it was keep their balance, much like how a cat uses their tail.

All the more so since whoever it was could run up the side of a building without any difficulty. The Cantus Bellax spell he had cast upon himself when this started could make someone faster and more agile, but running up walls was another thing entirely, as anyone who tried parkour could testify.

'Really wish Kotaro or Negi was here. They could run up that wall with no trouble at all. As it is...'

Gandolfini tried to run up the wall that the intruder ran up. He made it to the top, but the effort had cost him. As he got to his feet, the intruder stood on the far side of the roof both were on, ready to jump.

"Stop!"

The girl dressed as a ninja paused for an instant, then winked at him before jumping off.

'We're six stories up,' Gandolfini thought as he raced to the edge and looked over. To his credit, he was not completely surprised when he could not find her. He had been around Kaede and the Narutaki twins enough to know that they could disappear at a whim. How they did such, he still did not know.

 _She jumped off the roof of the high-school dorms. I've lost her._

Something exploded to his right, between another of the dorms and a building used as a meeting hall for the high-school girls. Whatever it was, it produced a lot of smoke.

 _Well, I DID find her. She used a smoke bomb though, and I can't see anything._

Gandolfini glanced around the smoke cloud, in hopes of spotting something moving even as Takamichi was telepathically admitting he lost the intruder. _She did not double back towards me anyway._

 _This is getting annoying._

He shuddered. Kuzunoha was not a little scary when she was upset. From the tone of the telepathic message, he could tell she was upset.

Takamichi agreed with her. _That's two times in two days. It's a shame Negi-kun isn't here. He could catch them easily._

 _Or Kotaro,_ Seruhiko added.

 _Negi-kun is unfortunately being a diplomat welcomed in the Hellas Empire at Theodora-hime's request. I believe Kotaro-kun is with him, but he is training at Negi's request. All of you, please come to my office. This needs to be discussed in private._

Gandolfini responded in the affirmative to Konoemon's request, and made his way to the roof access door. 'This will not be a pleasant meeting,' he thought.

* * *

.

Thirty minutes later Gandolfini stood next to Seruhiko, finishing up his own report about the intruders. The Headmaster had remained quiet through Seruhiko's report, as well as Takamichi's brief statements. Kuzunoha had also kept quiet, although she had voiced her doubts when the unusual ears and tails of the intruders were mentioned. Seruhiko confirmed his own story about the tail, although he had to admit that he had not gotten a good look at their heads enough to confirm his observation of the ears of the intruders.

"We know there was two of them yesterday as well. The question is, are these the same two as yesterday?" Gandolfini asked.

"I'm still wondering about the ears and tail," Takamichi admitted. "I know nothing like that either here or in the Magical World."

"The only thing that even comes close to that description would be those such as Poyo Rainyday. But even then..." Seruhiko started, before Konoemon held up his hand.

"For the foreseeable future, I am going to increase the security details around Mahora. I want every eye searching for any further intrusions. Kuzunoha can work out the details about shift changes and increased staff, as I want some of the more... _astute_ students to be patrolling as well."

He knew what that meant. Negi's students, as well as those from the Magical School would be involved in patrols. He glanced over at Kuzunoha and was unsurprised to see her expression darken at the request. He was surprised that she nodded in assent instead of objecting.

'She must still be annoyed about how they escaped from her yesterday,' he thought.

"I would prefer to capture them, so they can be questioned," Konoemon continued, "But if they use deadly force to defend themselves, then of course you are allowed as well. Are there any further questions?"

He shook his head as did everyone else.

Konoemon smiled, "Good. Perhaps I can perform a random patrol as well after I welcome in some transfer students first thing in the morning."

"Oh?" Takamichi asked.

The Headmaster nodded, "Five new students, two of them twins, will be attending Mahora Academy starting the first of the week. I am just going to give them a brief welcome before allowing them to explore the Academy so they will know their way around when they start classes."

"Do we need to worry about them?" Seruhiko asked.

"No. All of them are mundane," Kuzunoha replied.

"If there are no further questions," Konoemon paused, giving everyone a chance to ask a question. Upon hearing none he finished, "everyone is dismissed."

* * *

 _._

 _Elsewhere..._

"Well? What have you discovered so far?" came a female voice as two females dropped to the ground from their hiding place in the ceiling.

"For someplace to have so much Magic, there are too few defenders," the first replied.

"Indeed. I had two people chasing me at most. Only one of which could keep up," the second added.

"Ho ho ho! Do I sense someone plotting an 'assassination' mission soon?"

"Perhaps Demon Lord," the second said.

"Wait a while before you do that my dear. As much as I would celebrate your finding a husband, I still need your other abilities for a time. Do we know the source of the Magic here in this place?"

"A very large tree near the middle. We could feel it's power as we crossed over the walls," the first said

"Interesting. But you said yesterday that there were no druidic types tending to the tree. What sort of realm are we in, I wonder? Allow me to mention that while you two were scouting, I was acquiring this location as our base of operations here. I was getting ready to open the portal to allow our 'supplies' through. Is there anything you two need before I do so?"

"Perhaps..." the second one started.

The first one interrupted her, "Two more kunoichi to help with scouting and protection efforts, Demon Lord."

"Then both of you get some rest. I will need you to scout tomorrow as well. This time do not be discovered."

Both nodded their assent before departing.

"This is an interesting place. There is Magic, but it is not openly used from the look of things. I wonder why that is?"

"Perhaps you will find out if there are enough converts," said a male voice behind her. "I could try to scout this realm as well if you wished."

"I do not wish dear husband. I need you here with me helping make enough energy to convert the females of this Academy into our followers."

"As you wish my Lord and Wife."


	2. Day One

Negima is owned by Ken Akamatsu and Kodansha. Whoever created Monster Girl Encyclopedia owns the rest. I am making nothing off this.

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Chapter 1

Day One  
Friday

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Dean Konoemon smiled as he finished his welcoming speech, "I believe I have bored all of you enough. If you have questions, do not hesitate to ask me or anyone you may find. The students are usually quite happy to help welcome in new people. Especially if they can help keep someone from becoming lost within Mahora's walls."

"Lost?" asked one of the new students, someone who appeared to be transferring into the high school.

Konoemon nodded, "Mahora Academy is fairly large, and students have been known to get lost, not just within the buildings themselves, but on the grounds as well."

"Is that why there is..."

"A map in our welcoming package?"

Konoemon smiled, "It is indeed."

The twins in front of him had been interesting to listen to thus far. They had asked several questions, with one twin starting the question, and the other finishing it. He had heard of twins doing that, but this was the first time he had seen such a phenomenon. Konoemon noted that it was always the same twin that started the question or comment. He wondered if that one was the 'first' twin. Both were transferring into the same class in junior high.

"Do you two always speak like that?" asked another new student transferring into the junior high school.

Both twins nodded. "We have always..." started one.

"Spoken like this," finished the other.

Konoemon glanced down at the open folder containing information about the twins. Rin and Ran Yokota. Born almost two years after Konoka on one of the smaller islands surrounding Japan proper. Contact information had checked out, as well as the family itself. Yokota was an old name, much like the Konoe name itself, but respect for that name had diminished over time as had the number of those that carried the name. A quick check with an internet search engine had turned up more instances of the name in America than in Japan.

"Doesn't that bother people when you do that?" the inquisitive junior high transfer continued.

"It does sometimes at first. Especially the first week," Rin replied.

"But most everyone we are with becomes accustomed eventually," Ran said.

"Can you speak normally? I mean, both of you are not always together, so you must be able to speak when you are apart?" asked the final transfer student.

There was a pause before the second twin reached over to cover the first's mouth with her hand before replying in a halting tone, "We can, but... It is more... Difficult than... You might think."

"Wow," said the first girl. The other two just nodded in agreement.

"How do you..." Rin started.

"Think we feel?" finished Ran. Both sighed before Rin spoke again.

"We are usually not far apart."

"We even join the same club."

"What club is that?" asked the final transfer student.

Both twins glanced at each other before Rin replied, "We heard there was a club..."

"That was organized like a business," finished Ran.

Everyone glanced at Konoemon as he chuckled before saying, "The Capitalism Club. One of the few clubs that turns a profit each year. Each member is expected to come up with a product or two to sell, as well as a plan for the manufacture and distribution of that product. Becoming a member is a challenge in itself, but of those that join, the majority turn out to be quite the businesswomen. Both of you will have to demonstrate a business sense above and beyond what is normal perhaps, as membership is normally restricted to those in high school and above."

Both smiled as Rin said, "Considering that we have experience in selling...

"Woolen blankets, it should not be a problem," finished Ran.

"Wool blankets? I wouldn't think those would sell here?" asked the final transfer student.

"The blankets are specially woven to be extra soft and," started Rin.

"Keep whoever uses it warm and snug, encouraging a deep sleep," said Ran.

After a brief pause, Rin sighed, "It is a shame that we traded off the animals that made the wool ages ago."

Ran nodded, "Otherwise, we would have a ready product for the Capitalism Club to demonstrate our marketing skills."

The first transfer student shook her head, "I still cannot get used to how you two speak."

"I like it. They stand out from everyone else," smiled the final girl as she continued, "Have you both noticed that you each speak the same number of words? It is as if you split whatever you're saying right in half."

"It seems we," started Rin.

"Do that automatically," finished Ran.

After the briefest of pauses, Rin continued, "We have been accused of witchcraft several times because we speak like this."

"It is an observed fact that twins are alike in thought as well," finished Ran.

Konoemon clapped once to return everyone's attention to him before saying, "I know all of you are eager to hear your fellow transfer students speak, but I do have two announcements before I allow you to go exploring." As everyone turned to face him, he continued, "Today is Friday, and though classes have already started for today, you should acquaint yourselves with the location of your homeroom. I expect you to use the coming weekend to purchase supplies and get everything in order so that you can start attending classes Monday morning. I believe that I have sent each of your teachers a note saying that you would be ready to start then."

Everyone nodded in agreement.

Konoemon smiled as he continued, "Mahora Academy is widely known for encouraging individuals to learn things on their own, as well as self-reliance, but that does not mean you will not receive help if needed. If there are issues, please inform one of the staff so they can help you."

As the new students stared at him expectantly, he continued, "As it is the month of October, the student council petitioned me to permit those who wished to do so to wear cosplay until the end of the month. So please do not be alarmed if you spot fantasy or anime characters walking around. I myself have seen quite a few ninja in the past two weeks since I approved of the cosplay. You can even take part if you wish."

"So I can dress up as my favorite anime character?" asked the final transfer student as she bounced eagerly on her feet.

Konoemon nodded, "You can indeed, but I would wait until after you get settled here."

"But the end of the month is not far away. You're making me wish I had transferred earlier Headmaster-sama."

He chuckled, "Perhaps, but I would not go into your homeroom dressed in cosplay on your first day of classes."

"Then I can go shopping for books and supplies while dressed in cosplay," the final student smiled. "Let everyone see me in cosplay so they can clearly identify me as a student here."

He nodded again, "I suppose that would work. If there are no other questions, I will allow you to go forth to explore."

Everyone smiled as they left his office. It was obvious to Konoemon that they were all eager to discover all that they could about their new home. He wondered idly what product the twins would use to impress the Capitalism Club as he left to perform his own rounds.

* * *

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Shortly after classes had ended for the day, Natsumi found herself wandering into the town proper as the Drama Club was not meeting. Mahora Academy had plenty of places to shop, but she liked to go into town every so often, if only to see if there were new shops to visit.

She had not walked half a block before she spotted a new shop. One look at the sign hanging over the door told her exactly what was sold inside.

'Altered Forms Costume Shop?' Natsumi thought. 'I wonder if they are open?'

As she started towards the building, the front door opened to reveal an old woman with a broom coming outside. Upon seeing Natsumi, the old woman smiled and asked, "A potential customer. Are you curious about our costumes young lady?"

Natsumi nodded, "I am, but are you open yet?"

"We are still finishing up stocking our inventory, but you are welcome to come inside and take a peek if you wish?" the old woman said.

Natsumi smiled, "I'd like that. Especially since this is the season to have a costume."

"Then please come inside. After all, word of mouth is still the best method of attracting customers."

As Natsumi entered, she heard someone behind a counter. When Natsumi turned toward the noise, a figure looking like a much younger version of the old woman rose up to greet her.

"Hello," Natsumi said.

The figure opened her mouth to say something before spotting the old woman entering behind Natsumi. "Mother, we are not ready yet," she said.

"And that is my fourth daughter, Druella. Normally, I chide her for being impulsive, but today seems to be her day to chide me. And she will give me a lecture when she discovers that I have not done anything to advertise this shop."

Natsumi could see Druella's eyebrows shoot upward at that revelation, but the old woman kept talking as if nothing was the matter, "And as such, I decided to invite..." she looked at Natsumi expectantly.

"Murakami Natsumi," Natsumi replied, not realizing she had fallen into a classic sales trap.

"Natsumi-san here to browse the shop and help advertise our costumes. Hopefully she will find something that strikes her fancy so she can wear it around and show everyone exactly why we called this place 'Altered Forms.'"

Natsumi could see Druella sigh before she started in on her mother, "I know you appreciate word-of-mouth advertising over all other forms Mother, but we still need to..."

"Now, now my dear. Let Natsumi here get out of hearing before you start lecturing your mother." The old woman winked at Natsumi, "Go on dear. Look wherever you wish."

Natsumi smiled thankfully at the old woman before heading further into the store.

* * *

.

When Natsumi was safely out of earshot, Druella hissed, "Are you sure this is a good idea?"

"Could you feel her magic?"

Druella nodded, "I did, but..."

"But nothing. Fate has dropped someone into our laps. We are about to have our first new follower. I expect you to train her well after I finish 'recruiting' her.

"If you are sure of this, then I will obey," Druella replied.

"Of that I have no doubts. Now, time for me to have some fun," the old lady murmured before fading from view.

* * *

.

Natsumi made her way through several sections of costumes. She had passed by a large rack filled with what appeared to be various bird costumes. All of them were well made, with the wings appearing to be crafted carefully with real feathers and what felt like suede for the fake feet and claws for the ends of the arms. The sign above the rack stated this was "Harpies, Sirens, Gandharva, and More."

Natsumi wasn't sure what a Gandharva was, but a quick examination of a costume labeled as such told her that it was evidently a bird possessing large breasts. Embarassed, she moved onward in her search.

She passed a full rack of what appeared to be nun costumes, but one look at them revealed that even Misora would not even wear one of those. A rack labeled "Demihumans" looked promising to her, but another quick examination showed that they would not fit her very well. Those were obviously for more athletic girls, or at least those with bigger... assets.

Continuing her search for something that wouldn't embarrass her to wear, Natsumi pushed ahead between two very different racks of costumes. One rack was labeled "Wonderland costumes," with quite a few costumes clearly displayed of the sort that would be worn by those wishing to be Alice in Wonderland. There were several other costumes on the rack though, and a quick glance confirmed there were a few rabbit, cat, and mouse costumes as well. The other rack was a bit more sinister in appearance, being labeled "Imps, Devils, and Demons." Natsumi glanced at the costumes there and noted that most were little more than bits of leather and stockings with wings and horns. The only difference between "Devils" and "Demons" appeared to be size. Devils were much shorter, if the costume was any indication. Turning so that both racks were behind her, Natsumi wandered to the final rack labeled "Succubi costumes."

Natsumi frowned as she glanced at the costumes there. There were a few that could be called 'modest,' but the majority of the costumes she looked at had less material than the costumes on the "Imps, Devils, and Demons" rack. Natsumi examined one of the more modest costumes. It appeared to be made similar to a coat worn with a tuxedo, with a full tail that reached past Natsumi's knees and purple wings and flexible tail so dark in color they appeared to be almost black attached to the lower back.

 _Try it on._

Natsumi searched the shop until she found the changing rooms. Conveniently enough, they were not too far from where she was. 'There are so many. It's as if they expect over a dozen girls in here at once,' she thought. 'But then, Mahora is someplace where that would be possible, especially this close to Halloween.'

 _Try it on._

'I'm not sure why I'm doing this. I won't look pretty in this at all,' she thought as she made her way to the changing room closest to her. Stepping inside, she closed the door and locked it. Looking at her figure in the mirror set in the door, she sighed before starting to remove her clothes.

* * *

.

Druella heard the bell ring as the door opened. Turning from the rack she was putting more costumes on, she spotted two figures entering. She smiled before asking, "How was your day?"

"Long and tiring," said Rin.

"But ultimately rewarding," finished Ran.

"Oh? How so?" Deruella asked.

Before Rin could respond, there was a scream of pleasure from the back of the store, followed by a surge of power. Both twins looked at Druella with quizzical expressions on their faces. "Our Lord found someone that radiated magic, so she decided to recruit her. But that..." Druella peered at the changing rooms, "Felt like she did more than just recruit her."

"Well then, it is safe for..." started Rin.

"Us to drop our human images," finished Ran. The air around both twins shimmered before revealing their normal forms. The residents of Mahora Academy as well as the town outside would refer to them as tanuki, but if any referred to the twins as such, they would be gently corrected by them.

Gyoubu Danuki are rather proud of their forms after all.

"I hope no one outside felt that power," said Rin.

Ran nodded, "The Demon Lord used a lot just then."

"Perhaps I did, but as you will soon see, it was entirely worth it," came the old woman's voice. Seconds later, the Demon Lord stepped into view. Having cast aside her illusion for the moment, she strode forward proudly towards the trio of figures. When she was away from the various racks of costumes, she gestured grandly to the rear of the store, "May I present to you my first Lilim of this world?"

"Lilim?"

The Demon Lord smiled at Druella, "Calm yourself my dear. I did say that I felt magic coming from Natsumi. Well, I somehow tapped into it as I was converting her to our cause. Come out and let everyone see you Natsumi-san."

As everyone watched, a figure emerged from the changing room. Half hidden by the costume racks it slowly made its way to the front of the store. When it reached the area everyone was located, it spread its wings as if to show them off.

Druella chuckled quietly as she beheld the much changed Natsumi. Natsumi was no longer a redhead as her hair had turned purple with white highlights. Her new wings and tail had lightened into a shade of purple just darker than her hair. But the biggest change was not immediately obvious. When Natsumi entered the store, she was her normal shy and reserved self. The Natsumi that stood proudly before them was calm and confident as her poise showed.

Natsumi smiled in a way unlike her former self. "I was Murakami Natsumi, now Lilim Natsumi."

Druella bowed before replying, "I am Lilim Druella, Fourth Princess of the Demon Realm."

Both Gyoubu Danukis bowed to Natsumi, "We are pleased to meet you."

"I am Rin Yokota," said Rin.

"And I am Ran Yokota," said Ran.

"The Yokota Merchant Clan is quite influential in the realm we are from, but here the name is not as well-known. Rin and Ran wish to change that," the Demon Lord said. "Hopefully between all of us, we will be able to create a market for them."

"We suspect that Prisoner Fruit," started Rin.

"And Holstaurus Milk will be popular," finished Ran.

Natsumi giggled before asking, "Do both of you speak like that all the time?"

Both Gyoubu Danukis sighed before Rin said, "You really do not want to know how..."

"Many times we have been asked that today," finished Ran.

The Demon Lord interrupted then, "As much as I would like to listen and learn from our newest Mamono, I am afraid I need to replenish my magic with my husband. Druella, could you help train Natsumi for a while?"

Druella grinned, eager to please her mother, "I believe I can do so for a few hours at least."

"If that is the case, I better inform my roommate that I will be late getting back," Natsumi said.

"Oh?" the Demon Lord asked.

Natsumi turned to the Demon Lord and smiled, "Do not worry, my Lord. I plan on telling her that I have a new job. Which is not really a lie."

The Demon Lord appeared to be ready to nod her approval, but glanced upward at the ceiling suddenly. "Both of you, stop hiding and get down here."

Two figures landed on the ground in front of Natsumi and remained in a kneeling position. "We would like to welcome you to the Demon Lord's family," said one.

"Please use our services as you wish Lilim Natsumi," the other said.

Natsumi appeared surprised, "Ninja?"

"Kunoichi to be precise. They have been very busy for the past few days looking into everything about this Academy. Something I shall have to train you about," Deruella said.

"Ah. I see then. I suppose I should not be surprised as we have one of our own here," Natsumi said.

"Oh really?"

And with that, the author will leave the "training" and "information sharing" to the reader's imagination. Just assume that much information was shared and much training happened. Safer to do that than to describe it. Even if this story is rated Mature.

* * *

.

Chizuru was busy putting the final touches on dinner when Natsumi announced her return several hours later. As she went to the door to greet Natsumi, she noticed that Natsumi looked tired.

"My goodness. You look like you worked today," Chizuru said.

Natsumi nodded, "Not so much work as training. Lots of training."

"Well, where is this new job you have?"

"The new Altered Forms Costume Shop, Chizu-nee. You have to come with me tomorrow. You'll love it."

Chizuru chuckled, "If you say so. Dinner is almost ready."

"Then I will wash up as soon as I change out of my uniform." Natsumi hummed to herself as Chizuru watched her go to the restroom to change. She shook her head and thought, 'She is certainly happy she found a job with something she likes.'

Once inside the restroom, Natsumi resumed her new form. "Oh, I can't wait to introduce everyone. I wonder what forms everyone will take?"

* * *

.

Nimrod Notes

Posting this on the second of the month. I wanted to do this yesterday, but I finished only yesterday evening. Too exhausted to post after finishing, and wanting to make sure nothing was horribly wrong before posting.

I apologize for how long this took to complete. I haven't started on the next chapter yet, but I have notes for what I want.

For those that are curious as to what Natsumi looks like now: vahnyourdoomDOTdeviantartDOTcom/art/commish-ubernimrod-NatsumiLilim-554600321 Obviously, replace the DOTs. Vahn is a good artist, but he's moved on to now, so trying to get him for an individual commission is extremely difficult currently. If I wrote as fast as he worked, I'd be several chapters ahead by now.

STILL working on "Joker in the Deck." Getting the next chapter wrapped up is a minor pain as I am trying to make sure I include everything I need for later chapters.

Extra Note: No one complained about Deruella? Seriously? I edited it back to Druella, but I am really surprised that no one complained about my horrid spelling mistake there. But maybe I have it wrong.


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